The amount of printed matter is ever increasing, as is the requirement to read text on a computer screen accurately and efficiently. There are two elements to efficient reading namely reading speed, and comprehension of what is being read.
When reading, a reader's eyes move relative to stationary text. The reader's eyes do not move smoothly along the text, but rather perform a series of jerky movements consisting of jumps and stops. It is during the stops that information is taken into the brain. During reading, words tend not to be read one word at a time, but as a group of words along a line.
In the case of a poor reader, the jumps and stops do not flow along the lines of text, but sometimes backtrack and back skip. A backtrack is when the eyes jump backwards to what has been read, and a back skip is when the eyes jump backwards more than just the last group of read words. The back skip can be along a line, over several lines, or even may be a paragraph of the text.
In the case of a good reader though, the eyes are trained to move with longer jumps and hence there are less stops, for there are shorter pauses for the stops, and less or no backtracking or back skipping. Such eye movements enable information to be more smoothly conveyed to the brain, such improved presentation enables improved comprehension of the text being read.
It is common practice for a reader to use a pointer whilst reading, the pointer pointing to individual words as they are read.